Electronic assembly with one or more heat sinks

ABSTRACT

An electronic assembly comprises a semiconductor device that has conductive pads on a semiconductor first side and a metallic region on a semiconductor second side opposite the first side. A lead frame provides respective separate terminals that are electrically and mechanically connected to corresponding conductive pads. A first heat sink comprises a first component having a mating side. A portion of the mating side is directly bonded with the metallic region of the semiconductor device. A circuit board has an opening for receiving the semiconductor device. The lead frame extends outward toward the circuit board or a board first side of the circuit board.

This document claims priority based on U.S. provisional application Ser.No. 62/115,719, filed on Feb. 13, 2015 and entitled ELECTRONIC ASSEMBLYWITH ONE OR MORE HEAT SINKS, under 35 U.S.C. 119(e).

FIELD OF DISCLOSURE

This disclosure relates to an electronic assembly with one or more heatsinks for dissipating thermal energy from the electronics assembly.

BACKGROUND

In certain prior art, an electronic assembly may have a restrictedmaximum operating power capacity because of limited thermal dissipation.If semiconductor devices in the electronic assembly are operated beyondtheir maximum operating power capacity, the electronic assembly may failprematurely or be unreliable. For example, an electronics assembly withlimited thermal dissipation might be applicable to a lesser power rangeof electric motors or generators than otherwise possible. Accordingly,there is need for an electronic assembly with improved thermaldissipation to increase or optimize the maximum operating powercapacity.

SUMMARY

In accordance with one embodiment of the disclosure, an electronicassembly comprises a semiconductor device that has conductive pads on asemiconductor first side and a metallic region on a semiconductor secondside opposite the first side. A lead frame provides respective separateterminals that are electrically and mechanically connected (e.g.,directly bonded) to corresponding conductive pads. A first heat sinkcomprises a first component having a mating side (e.g., substantiallyplanar side). A portion of the mating side is directly bonded with themetallic region of the semiconductor device. A circuit board has anopening for receiving the semiconductor device. The lead frame extendsoutward toward the circuit board or a board first side of the circuitboard. Board conductive pads are on the board first side of the circuitboard to align with the corresponding terminals of the lead frame forelectrical connection therewith.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an electronic assembly.

FIG. 2 is a perspective exploded view of the electronic assembly of FIG.1 with a portion cut away to reveal the interior of various components.

FIG. 3 is a perspective exploded view of the electronic assembly of FIG.1.

FIG. 4 is top plan view of the semiconductor device and circuit board ofthe electronic assembly along reference line 4-4 in FIG. 3.

FIG. 5 is cross sectional view of a first embodiment of the electronicassembly along reference line 5-5 in FIG. 4 and further includingpassive heat sinks.

FIG. 6A is cross sectional view of a second embodiment of the electronicassembly along reference line 5-5 in FIG. 4 and further includingpassive heat sinks.

FIG. 6B is cross sectional view of a third embodiment of the electronicassembly along reference line 5-5 in FIG. 4 and further includingpassive heat sinks.

FIG. 7 is cross sectional view of a fourth embodiment of the electronicassembly along reference line 5-5 in FIG. 4 and further includingpassive heat sinks.

FIG. 8 is cross sectional view of the electronic assembly alongreference line 8-8 in FIG. 1.

FIG. 9 is cross sectional view of the electronic assembly alongreference line 9-9 in FIG. 1.

FIG. 10 shows a block diagram of the assembly that shares a coolantsystem of an internal combustion engine or hybrid vehicle.

Like reference numbers indicate like elements throughout the drawings.

BRIEF DESCRIPTION

An electrical and mechanical connection between metal or alloycomponents or structures may be formed by soldering, brazing, fusing,welding, or applying conductive adhesive. Directly bonded refers to anelectrical and mechanical connection, between the same or similar metalsor alloys, or between compatible (but different) metals or alloys, thatis formed by application of certain processes. Directly bonded refers toa bond, fusion, weld, or other electrical and mechanical connectionbetween the same or similar metals or alloys, or between compatiblemetals or alloys from heat, pressure, ultrasound, reactive bonding,vapor-phase bonding, or other techniques.

Direct bonding may be accomplished by one or more of the followingtechniques that may be applied cumulatively or separately. Under a firsttechnique of direct bonding, if the lead frame and the device pads arecomposed of copper or a copper alloy, the lead frame may be directlybonded to the device pads by direct copper-to-copper thermo-compressionbonding or ultrasonic bonding. Thermo-compression bonding refers to thesimultaneous application of pressure and heat to the materials to bejoined.

Under a second technique of direct bonding, reactive bonding refers toan exothermic chemical reaction triggered by application of thermalenergy from a reactive multilayer foil (e.g., of nickel and aluminum) tojoin the materials by creation of a new metallic material or alloy(e.g., nickel-aluminide). For example, the multilayer foil may be formedby sputtering thin alternating metal layers (e.g., nickel layers andaluminum layers), where each layer may be deposited to a thickness equalto or less than target thickness. At the time of preparing thisdocument, suitable reactive multilayer foils (e.g., for direct bondingof a heat sink to a metallic region) were sold by the Indium Corporationunder the trade name NanoFoil®.

Under a third technique of direct bonding, vapor-phase bonding methodsmay be used to bond a metal or alloy (e.g., copper) to siliconsemiconductors using a vapor-deposition of a priming intermediate metallayer (e.g., tin) to form an intermetallic compound (e.g., copper-tincompound or alloy) at the joint, where the intermetallic compound mayhave lower thermal electrical and thermal resistance than a comparablesolder joint. The vapor-phase bonding may require introducing anintermediate metallic material (e.g., tin) between the metal materialsto be joined with application of heat or pressure, or both. Theintermediate metallic material may have a lower melting point thanmetals or alloys to be electrically and mechanically connected.

For efficient thermal conduction, adjoining parts of the electronicassembly are joined to minimize thermal resistance and maximize heattransfer or thermal conductance between the adjoining parts. Thermalconductance may be enhanced by the manner in which parts of theelectronic assembly 10 are connected or bonded. Direct bonding typicallyoffers greater thermal conduction than a mere connection by soldering,conductive adhesive, or by contact between components with conductivegrease. In general, “bonded” or “bonding” refers to parts of theelectronic assembly 10 that are connected together or joined by adhesive(e.g., conductive adhesive or thermally conductive adhesive), soldered,brazed, or welded, whereas “direct bonding” results from the applicationof specific processes or techniques that reduce electrical and thermalresistance of the joint.

In accordance with one embodiment of the disclosure, FIG. 1 through FIG.3, inclusive, illustrate an electronic assembly 10. In accordance withone embodiment of the disclosure, an electronic assembly 10 comprises asemiconductor device 48 (FIG. 3, FIG. 4 and FIG. 5) that has conductivepads 66 on a semiconductor first side 72 and a metallic region 266 on asemiconductor second side 74 opposite the first side 72. Thesemiconductor device 48 may comprise one or more power semiconductordevices. A lead frame 16 provides separate terminals (e.g., supplementalterminals 58, and terminals 52, 54, 56) that are electrically andmechanically connected (e.g., directly bonded) to correspondingconductive pads 66.

A first heat sink 30 comprises a first component 37 (e.g., heatexchanger or passive heat sink) having a mating side 62 (e.g.,substantially planar side) and an opposite side opposite the mating side62. A portion of the mating side 62 is directly bonded with the metallicregion 266 of the semiconductor device 48. A circuit board 60 (in FIG. 3or FIG. 4) has an opening 20 for receiving the semiconductor device (48or 148 in FIG. 7). The lead frame 16 extends outward toward the circuitboard 60 or a board first side 76 of the circuit board 60. A boardsecond side 78 of the circuit board 60 is opposite the board first side78. Board conductive pads 18 or metallic terminations of conductivetraces 19 are on the board first side 76 of the circuit board 60 toalign with the corresponding terminals (52, 54, 56, 58) of the leadframe 16 for electrical connection therewith. In one illustrativeconfiguration, the lead frame may be constructed of copper base or corethat is plated with a metal or alloy interface layer (e.g., silver, goldor nickel, or alloys of any of the foregoing metals).

A second heat sink 12 comprises a first member (44 or 144) having amating side 64 (e.g., substantially planar side) and an opposite sideopposite from the mating side 64. In certain embodiments, the matingside 64 is in thermal communication (e.g., via a dielectric layer orthermal interface material 506) with at least a portion of thesemiconductor first side 72 or at least an interfacing surface of theterminals (52, 54, 56), where the conductive pads (54, 56) may bedirectly bonded to corresponding different ones of the device conductivepads 66. Further, in one embodiment, both the auxiliary metallic region166 and one or more device conductive pads 66 associated with analternating current output of a semiconductor device 48 are bonded(e.g., soldered) or directly bonded to output terminal 56. Theconductive pads 66 and auxiliary metallic regions (266, 366) are show inphantom or dashed lines in FIG. 4 because they are located below theterminals (52, 54, 56).

The lead frame 16 may be directly bonded to the device pads 66 and oneor more available auxiliary metallic regions (166, 366, if present) ofthe semiconductor device 48. If the internal circuitry of thesemiconductor device 44 affords the opportunity, multiple respectivedevice pads 66 can be interconnected to a same corresponding terminal(52, 54, 56) to increase the current capacity of the semiconductordevice 48 as illustrated in FIG. 4. For example, in FIG. 4 among theterminals the output terminal 56 is connected to an output phase of aninverter and is directly bonded to at least two conductive pads 66 anauxiliary metallic region 166 on the semiconductor first side 72, andauxiliary metallic region 366, where the output terminal 56 has asurface area that covers or overlies a majority of the first side 72 ofthe semiconductor device 48 where the output terminal 56 has a greatersurface area than a lesser aggregate surface area of the direct currentterminals (52, 54).

In various embodiments, as best illustrated in FIG. 4 through FIG. 7,inclusive, the electronic assembly 10 comprises one or moresemiconductor devices (48, 148) Each semiconductor device (48, 148) maycomprise one or more insulated-gate, bipolar transistors (IGBT's); powerfield-effect transistors (FET); power switching diodes, integratedcircuits chips, transistors with diodes coupled to the collector,emitter or both; or field effect transistors with diodes coupled to thesource, drain or both. For example, the semiconductor device 48 maycomprise at least two power switching transistors, alone or withassociated protective diodes, that are configured to provide one phaseof an inverter for outputting an alternating current signal or pulsewidth modulated (PWM) signal for controlling a motor, supporting agenerator, or supporting another electric machine.

Each semiconductor device (48, 148) may comprise one or moresemiconductor dies (50, 150) and a lead frame 16 (or substrate 505),where the semiconductor dies are semiconductor materials that arefabricated to form one or more transistors, diodes or circuits. Thesemiconductor device 48 may be formed of a semiconductor die (50, 150)such as a silicon carbide semiconductor die. The lead frame 16 providesseparate terminals (52, 54, 56, 58) that are electrically andmechanically distinct from each other. The terminals are connected toappropriate corresponding device conductive pads 66 on the semiconductordevice 48 to access its internal circuitry. The lead frame 16 provides agroup of separate direct current terminals (52, 54) for direct currentsupply to the semiconductor devices (48, 148) and an output terminal(56) for an alternating current output. In one embodiment, the firstterminal 52 and the second terminal 54 comprise terminals of the directcurrent bus and the third terminal 56 comprises an alternating currentoutput phase (e.g., coupled to the source and drain node of field effecttransistor pairs of an inverter phase circuit or the collector andemitter of bipolar transistor pairs of an inverter phase circuit) for aninverter. However, in other embodiments, the functions of the terminals(52, 54, 56) can be different.

In one configuration as shown in FIG. 4 and FIG. 5, the output terminalor third terminal 56 may be mechanically and electrically connected to(e.g., directly bonded to) one or more auxiliary metallic regions (166,366), where each auxiliary metallic region (166, 366) represents anoversized conductive pad (in comparison to conductive pads 66) on thesemiconductor die (50, 150) or package. Similarly, the first terminal 52and the second terminal 54 may be mechanically and electricallyconnected to (e.g., directly bonded to) other corresponding metallicregions or oversized conductive pads (in comparison to conductive pads66).

In one embodiment, the lead frame 16 has supplemental terminals 58 forone or more of the following signals: control, biasing circuitry,protection circuits (e.g., diodes), sensor support, data communications,or other functions. The supplemental terminals 58 of the lead frame 16extend outward from the package 501 of the semiconductor device 48; thesupplemental terminals 58 may be connected to corresponding deviceconductive pads 66 (in FIG. 4). As shown in FIG. 4, the semiconductordevice 48 has device pads 66 around a periphery of the semiconductordevice 48 and one or more metallic regions (166, 366) only occupy acentral region of the semiconductor device 48.

One or more lead frames 16 can eliminate requirements for wire-bonds tothe semiconductor die (50, 150); can provide optimized parameters forelectrical characteristics such as minimized values of stray inductanceand stray capacitance offered by circuitry (e.g., of a phase of thepower inverter). Elimination of bond-wires and replacing them with thelead frame 16 can reduce overall cost of the semiconductor device 48 ofthe electronic assembly 10 and can reduce premature failures caused bywire-bond fatigue, for example.

In an alternate embodiment, the terminal 56 may have an optional notch99 in its interfacing surface to provide stress relief (e.g., fordifferences in thermal expansion of various materials) or to provideaccess for insertion of potting material (e.g., polymer, elastomer orplastic). The optional nature of optional notch 99 is indicated by thedashed lines in FIG. 3. The optional notch 99 may be generally V-shapedor U-shaped, for example. In one embodiment, the notch 99 providessavings of metallic material and amply supports the output current thatflow outwards to an outer portion of the third conductive terminal 56(e.g., alternating current terminal) that is connected to conductive pad18. Regardless of whether the optional notch 99 is present or absent,electrical current doesn't need to flow or concentrate in the triangularregion defined by the notch 99 to supply an outer portion of terminal 56with adequate current. Therefore, if the metallic material is taken out(or chopped out) to create optional notch 99, the notch 99 doesn'tdisrupt or impede current flow in the electronic device or inverter.

In one embodiment, the presence of notch 99 helps mitigate anycoefficient-of-thermal-expansion (CTE) mismatch between one or moreprimary semiconductor dies (50,150) on left-side of FIG. 4 and one ormore secondary semiconductor dies on the right-side of FIG. 4, where theprimary semiconductor dies or secondary semiconductor dies are active atdifferent times and may have different duty cycles. Either the primarysemiconductor dies (e.g., low-side semiconductor switches) or thesecondary semiconductor dies (e.g., high-side semiconductor switches)supply current (e.g., alternating current inverter phase output signal)to the outer portion of terminal 56 and the conductive pad 18.Typically, the primary semiconductor dies and the secondarysemiconductor dies do not provide current to terminal 18 simultaneously.Therefore, if a primary semiconductor die or dies heats the left-side ofthe electronics device 10 because of a greater duty cycle, activity orother reasons, the right-side semiconductor die or dies may be closer tointernal ambient temperature, or vice versa. During operation of theelectronic assembly or inverter, a differential temperature between theprimary semiconductor dies and secondary semiconductor dies that couldotherwise lead to CTE-related issues are mitigated by the presence ofnotch 99.

FIG. 4 is top plan view of the semiconductor device 48 and circuit board60 of the electronic assembly 10 along reference line 4-4 in FIG. 3. InFIG. 3 and FIG. 4, first conductive strip 402 on a board first side 76of the board 60 is connected to the first terminal 52 at conductive pad18 and has a sufficient size (e.g., width and thickness of metal, alloyor metallic material, such as a heavy copper pour) to carry the requireddirect current supply demanded by each semiconductor device 48 at thecorresponding operating voltage and to promote secondary heatdissipation from the first terminal 52. The second conductive strip 401on a board second side 78 of the board 60 is connected to the secondterminal 54 at conductive pad 18 (e.g., through a conductive via orblind via) and has a sufficient size (e.g., width and thickness ofmetal, alloy or metallic material) to carry the required direct currentsupply demanded by each semiconductor device 48 at the correspondingoperating voltage and to promote secondary heat dissipation from thesecond terminal 54. A third conductive strip 403 lies on the boardsecond side 78 and is connected to the third terminal 56 at conductivepad 18 (e.g., through one or more conductive vias or blind vias). In oneembodiment, the third conductive strip 402 has a sufficient size (e.g.,width and thickness of metal, alloy or metallic material) to carry therequired alternating current output or pulse-width modulation signal(e.g., to control one phase of an electric motor) and to promotesecondary heat dissipation from the third terminal 56.

The first conductive strip 402 on a board first side 76 of the board 60and the second conductive strip 401 on a board second side 78 of theboard 60 overlap spatially (but separated by the dielectric layer of theboard) to minimize loop inductance. Minimization of loop inductancecaused by power traces on board 60 allows power semiconductor devices(48, 148) to switch faster and reduce energy loss to due reduction inswitching time. Reduction in energy loss helps increase inverterefficiency and results in fuel savings for hybrid vehicles that use fuelfor an internal combustion engine. Reduction in loop inductance tends toreduce over-voltage across DC terminals (52 and 58) and at output ACterminal (56), which can increase life of power semiconductor devices(48) and longevity of insulation system of electric motor drive byinverter or electronic assembly 10. Therefore, the proposed packagingconcept results in an electronic assembly 10 or inverter system thatoffers energy/fuel savings and increased reliability of the electricdrive system because of potential or actual reductions in the electricalstress, thermal stress, or both.

In one alternate embodiment, the first conductive strip 402, the secondconductive strip 401 and the third conductive strip 403 may be thermallyconnected the first heat sink 30, the second heat sink 12, or an outerenclosure or cover of the electronic assembly by using high-voltagedielectric and high-thermal conductivity TIM (thermal interfacematerial).

A current sensor 91 is located on the board first side 76 above thethird conductive strip 403 to sense the alternating output currentcarried by the conductive strip 403 or outputted by the semiconductordevice 48 (e.g., for a single inverter phase at output terminal 56). Thecurrent sensor 91 may be associated with ferrite members 93 on each sideof the current sensor 91. The current sensor 91 and the ferrite members93 are surrounded by a metallic shield 409 to shield the current sensor91 from electromagnetic interference or noise that might otherwisedegrade the sensitivity or performance of the current sensor 91. Themetallic shield 409 may conform to the size and shape of the currentsensor 91, alone or together with the ferrite members 93, above circuitboard 60 with a generally uniform spatial gap between the metallicshield 409 and the current sensor 91 for mechanical clearance. Forexample, the metallic shield 409 may conform to the size and shape ofthe current sensor 91, alone or in combination with ferrite member 93,that is substantially polygonal with an opening in its bottom abovestrip 403. The metallic shield may be formed of one or more sections ofmetal screen, metallic material, or fabricated sheet metal. In oneconfiguration, the metallic shield 409 may be integral with, secured to,or molded with an housing member of an enclosure cover that covers atleast a top portion of the electronic assembly.

The current sensor 91 and shield 409, which can be incorporatedintegrally into an upper case or housing cover, is capable of shieldinga surface-mount current sensor 91 to sense alternating current poweroutput at output terminal 56. The shielding eliminates noise andinteraction among sensors for different phases making inverter operationfree from noise that occurs when non-core (magnetic core) based sensorsare placed over alternating current strip or bus bar.

In an alternate embodiment, the first conductive strip 402, the secondconductive strip 401, and the third conductive strip 403 can be replacedby metal bus bars or laminated metal members (e.g., metal bus bars) withan intermediate dielectric layer.

FIG. 5 is cross sectional view of a first embodiment of the electronicassembly along reference line 5-5 in FIG. 4 and further includingpassive heat sinks (144, 37) or heat exchangers. In FIG. 5 and FIG. 6,the first member 144 (e.g., heat exchanger or passive heat sink) of thesecond heat sink 12 is electrically isolated from the lead frame 16 by athermal interface material 506, a dielectric layer, or a dielectricadhesive. In some configurations, the second heat sink 12 may beconnected to vehicle or chassis ground. A thermal interface material 506(TIM) sheet or layer is placed between top surface of lead frame 16 andsecond heat sink 12. In one embodiment, the TIM layer 506 is composed ofa dielectric material or sheet that is adhesively bonded to the leadframe 16, the second heat sink 12 or both. The first member 144 of thesecond heat sink 12 is electrically isolated or insulated from one ormore terminals (52, 54 and 56, or at least terminal 56) by the thermalinterface material 506.

In the first heat sink 30, first protrusions 34 extend from the firstbase portion 32, such as a metallic plate. In the second heat sink 12,second protrusions 40 extent from the second base portion 14, such asmetallic plate. The first protrusions 34 and the second protrusions 40are arranged to dissipate thermal energy or heat from the semiconductordevice 48 on both sides (72, 74) of the semiconductor device 48.

In FIG. 5, FIG. 6A and FIG. 7, the first component 37 (e.g., heatexchanger or passive heat sink) of the first heat sink 30 may be bondedor directly bonded to the a metallic region 266 on the device secondside 74 (e.g., bonding surface or bottom surface) of the semiconductordevice 48 or die (50, 150). For example, the direct bonding supports alow resistance to thermal conductivity from the semiconductor device 48to the first component 37 or first heat sink 30. The metallic region 266may be formed of copper, silver, gold, nickel or an alloy, for example.Alternately, the metallic region 266 may have a silver, gold or nickellayer that overlies a copper core. Similarly, the mating side 62 firstcomponent 37 and the mating side 64 of the first member (44 or 144) maybe plated with silver, gold, nickel, or any alloy of the foregoingmetals or a combination of the foregoing metals to facilitate bondingwith the first component 37 and the first member (44 or 144).

The first component 37 or first heat sink 30 may be directly bonded tothe metallic region 266 on the semiconductor device 48 by directcopper-to-copper, thermo-compressive bonding or ultrasonic bonding tobond a metallic layer 266 on the device second side 74 (e.g., bottom) ofsemiconductor package 501 to the first heat sink 30, or its firstcomponent 37, another suitable technique of direct bonding, such asreactive or vapor-phase bonding. The metallic region 266 (e.g., coppermetallization region) on a device second side 74 (e.g., bottom) ofsemiconductor device 48 could be at ground or floating potential. Themetallic region 266 can dissipate or transfer heat from thesemiconductor device 48 to the first component 37 or the first heat sink30. Similarly, the auxiliary metallic region 166 and pads 66 candissipate or transfer heat from the semiconductor device 48 to thesecond member 42 of the second heat sink 12 or its first member 144. Thepresence of both auxiliary metallic region 166 and one or more pads 66for any corresponding terminal provides potentially greater heatdissipation and current carrying capacity of the terminal than for aterminal of smaller size and dimensions.

In one embodiment, the first member (44, 144) is formed of a metallicmaterial, an alloy or metal, for example. However, in certainembodiments, the first member 44 may be formed of a dielectric material,such as ceramic. In certain configurations, the second member 42 may beformed of plastic, polymer, or a fiber-filled plastic or polymermaterial.

FIG. 6A is cross sectional view of a second embodiment of the electronicassembly along reference line 5-5 in FIG. 4 and further includingpassive heat sinks. The electronic assembly of FIG. 6 is similar to theelectronic assembly of FIG. 5, except first member 44 of FIG. 6Areplaces first member 144 of FIG. 5 and TIM 506 has a greater size,shape and surface area commensurate with that of the first member 44.The first member 44 may overlie the terminals (52, 54, 56). In contrast,the first member 144 of FIG. 5 may be narrower in width and may onlyoverlie the third terminal 56 (output terminal). The first member 44 ofthe second heat sink 12 is electrically isolated or insulated fromterminals (52, 54 and 56) by the thermal interface material 506. In FIG.6A, the first heat sink 30 is bonded or directly bonded to the metallicregion 266.

The configuration of FIG. 6B is similar to the configuration of FIG. 6A,except a thermally conductive adhesive 508 is used between the metallicregion 266 (or the second surface 74) and the first component 37 of thefirst heat sink 30. The semiconductor device 48 and the first heat sink30 may be directly bonded, bonded or connected by thermally conductiveadhesive 508. If thermally conductive adhesive is used, it is possibleto omit the metallic region on the bottom of the semiconductor device 48of FIG. 6B and extend the package 501 around the bottom of thesemiconductor device 48.

FIG. 7 is cross sectional view of a fourth embodiment of the electronicassembly along reference line 5-5 in FIG. 4 and further includingpassive heat sinks. The electronic assembly of FIG. 7 is similar to theelectronic assembly of FIG. 5, except the thermal interface material 506and the lead frame 16 are replaced by the substrate 505 with itsconductive trace terminals (504, 507) and its dielectric layer 502(e.g., ceramic, polymer or composite). The conductive traces (504, 507)of the substrate comprise an output terminal 504 that is analogous tooutput terminal 56 on the electronic assembly of FIG. 5. For example,the output terminal 504 may represent the alternating current output ofone phase of the inverter. The output terminal 504, or its interfacingsurface, is bonded (or directly bonded) to one or more conductive pads66 of the semiconductor device 48 and an auxiliary metallic region 166on the device first side 72; the mating surface 510 of the outputterminal 504 is electrically and mechanically connected to one or moreconductive pads 18 on the circuit board 60. Similarly, the terminal 507is bonded (or directly bonded) to one or more conductive pads 66 of thesemiconductor device 48; the mating surface 510 is electrically andmechanically connected to one or more conductive pads on the circuitboard 60. The output terminal 504 is connected to a correspondingconductive strip 402 (e.g., on the circuit board 60), where theconductive strip 402 has sufficient size to promote secondary heatdissipation from the output terminal 504. In certain configurations, theoutput terminal 504 is connected to a corresponding metal strip (e.g.,conductive strip 402) on the circuit board for heat transfer from theoutput terminal 504 to the metal strip.

As shown in FIG. 5 through FIG. 7, inclusive, the bottom, sides, or airgaps below the lead frame of the semiconductor device are encapsulatedwith plastic, polymer, resin, or plastic or polymer with a suitablefiller material, which may be referred to as package 501. Encapsulationof the semiconductor device reduces assembly pollution, increasesdimensional stability in response to thermal or mechanical stress, andavoids arcing or flash-over when the semiconductor device is operatingat high operational voltage (e.g., 800 Volts plus nominal, plustransient voltage spikes). The semiconductor devices (48, 148) in FIG. 5through FIG. 7 may be used in a passively cooled mode without forming orproviding the coolant passages, chambers or interiors for circulatingcoolant within the complete electronic assemblies 10 of FIG. 1-3, FIG. 8and FIG. 9.

The electronic assembly 10 (or its semiconductor device 48, 148) of thisdisclosure allows thermal energy to be conducted efficiently away fromthe semiconductor device 48 to the first heat sink 30 (or its firstcomponent 37), the second heat sink 12 (or its first member 44 or 144),or both through one or more thermal pathways of the electronic assembly.In a first example, a first thermal pathway represents a thermallyconductive path from the die (50, 150) via a metallic region 266 that isbonded or directly bonded to the first heat sink 30. In a secondexample, the first thermal pathway represents a thermally conductivepath from the die (50, 150) via a metallic region 266 (or package 501)that thermally communicates with the first heat sink 30 through athermal interface material 506 or thermally conductive adhesive. In athird example, a second thermal pathway represents a thermallyconductive path from the die (50, 150) via one or more device conductivepads 66 and one or more metallic regions (166, 366) to the outputterminal 54 (oversized alternating current terminal) that: (a) isconnected (e.g., bonded or directly bonded) to conductive traces (e.g.,strip 403 or heavy copper pours) of appropriate size for current andpower of the output alternating current, and (b) thermally communicatesto the second heat sink 12 (or its first member 44, 144) via a thermalinterface material 506 or dielectric layer. For example, the thermalinterface material 506 may be selected to have a certain minimum thermalconductivity or a target range of thermal conductivity. In oneembodiment, the first thermal pathway and the second thermal pathwaypromote adequate heat dissipation for the semiconductor device 48 towork at a target power capacity rating at a desired duty cycle orcontinuous duty cycle.

Referring to FIG. 1 through FIG. 3, FIG. 8 and FIG. 9, the electronicassembly 10 comprises a first heat sink 30, a second heat sink 12, orboth. A passively cooled heat sink may transfer, remove or conduct heator thermal energy away from one or more semiconductor devices 48 toambient air. An actively cooled heat sink may use a coolant or liquid totransfer heat or thermal energy from one or more semiconductor devices48 by circulating coolant via a pump (e.g., pump 243 in FIG. 10) to aradiator (e.g., radiator 246 in FIG. 10), or by circulating air via afan, for example. In certain embodiments, as illustrated in FIG. 5through FIG. 7, the first heat sink 30 or the second heat sink 12 cancomprise a passively cooled heat sink (e.g., cold plate). However, ifthe first heat sink 30 is used in conjunction with additional componentsof FIG. 1 through FIG. 3, inclusive, and FIG. 8, FIG. 9 and FIG. 10, thefirst heat sink 30 may operate as an actively cooled heat sink.Similarly, if the second heat sink 12 is used in conjunction withadditional components of FIG. 1 through FIG. 3, inclusive, and FIG. 8,FIG. 9 and FIG. 10, the second heat sink 12 may operate as an activelycooled heat sink. If operated as an active heat sink, the second heatsink 12 and the first heat sink 30 may each comprise an enclosure forreceiving a liquid coolant.

Throughout this document, a heat sink may refer to one or more of thefollowing: a first heat sink 30, the second heat sink 12; a portion ofthe first heat sink 30, such as the second component 35; and a portionof the second heat sink 12, such as the second member 42. The heat sinkmay comprise a passive or active: first heat sink, second heat sink, orboth. A passive heat sink may be cooled by ambient air, whereas theactive heat sink may be cooled by coolant that is circulated orcirculated air, for example.

In one embodiment, first heat sink 30 comprises a first component 37 anda second component 35 with a recess 28. The first component 37 and thesecond component 35 mate to form an interior volume 80, which is definedpartially by the recess 28. A seal 96 (e.g., gasket, sealant, or seal,such as illustrated in FIG. 8 and FIG. 9) may intervene between thefirst component 37 and the second component 35 to provide a hermetic orliquid-tight seal such that coolant or liquid in the interior chamber 33does not leak or escape into an outside or ambient environment. In oneembodiment, a plate 70 with a slot or aperture 26 may be disposedbetween the first component 37 and the second component to reduce thehydraulic pressure or forces that would otherwise be exerted (e.g.,upward against the first component 35 from the coolant to prevent thefirst base 32 from deforming, bulging or bending). In certainconfigurations, the second component 35 may be formed of plastic,polymer, or a fiber-filled plastic or polymer material.

In one embodiment, the first component 37 of the first heat sink 30comprises a lid or first base 32 with first protrusions 34 (e.g.,thermal dissipation members) extending from one end. First protrusions34 may refer to fins, ridges, pins, elevated islands, or protrusions forheat dissipation. First protrusions 34 comprise thermal dissipationmembers that can populate the interior volume 80 and that are generallyspaced apart from each other. The first protrusions 34 extend from thefirst base portion 32, such as a metallic plate. In certainconfigurations, the base portion 32 may comprise a generally planarmember of a generally uniform thickness. If coolant or liquid iscirculated within the interior volume 80, the first protrusions 34facilitate heat transfer from the semiconductor devices 48 to thecirculated coolant for removal via a radiator (e.g., 246 in FIG. 10) orheat exchanger to ambient air or otherwise.

The first heat sink 30 features at least two ports 36: an inlet and anoutlet for a first heat sink 30. The ports 36 are arranged forcommunication with the interior volume 80 to circulate a liquid coolantwithin the interior volume 80 of the first heat sink 30. Each port 36may be associated with a corresponding connector 38 to allow conduit ortubes to be attached thereto for connection to a pump, radiator, or bothto circulate the coolant within the interior volume 80 and to removethermal energy from the coolant to ambient air via the radiator.

In one embodiment, the second heat sink 12 further comprises a secondmember 42 that mates with the first member 44 to form an interiorchamber 33. For example, the second heat sink 12 may comprise a firstmember 44 (e.g., first housing member) that mates with a second member42 (e.g., second housing member) to form the interior chamber 33. A seal98 (e.g., gasket, sealant, or seal, such as that illustrated in FIG. 8and FIG. 9) may intervene between the first member 44 and the secondmember 42 to provide a hermetic or liquid-tight seal such that coolantor liquid in the interior chamber 33 does not leak or escape into anoutside or ambient environment.

One side of the first member 44 (e.g., heat sink or heat exchanger)comprises second protrusions 40 for heat dissipation. Second protrusions40 may refer to fins, ridges, pins, elevated islands, or protrusions forheat dissipation. The first member 44 comprises the combination of thefirst base 14 and the second protrusions 40. The first member 44 can beused as a passive heat sink in the absence of the second member 42.

In one embodiment, in the second heat sink 12 second protrusions 40 orother thermal dissipation members populate the interior chamber 33 andare generally spaced apart from each other. The second protrusions 40extend from a first base 14. In certain configurations, the first base14 may comprise a generally planar member of a generally uniformthickness. If coolant or liquid is circulated within the interiorchamber 33, the second protrusions 40 facilitate heat transfer from thesemiconductor devices 48 to the circulated coolant for removal via aradiator (e.g., 246 in FIG. 10) or heat exchanger to ambient air orotherwise. The second heat sink 12 features at least two ports 36: aninlet and an outlet for a second heat sink 12.

The ports 36 of the second heat sink 12 are arranged for communicationwith the interior chamber 33 to circulate a liquid coolant within theinterior chamber 33 of the second heat sink 12.

FIG. 8 is cross sectional view of the electronic assembly alongreference line 8-8 in FIG. 1. FIG. 9 is cross sectional view of theelectronic assembly along reference line 9-9 in FIG. 1. Like referencenumbers in FIG. 8, FIG. 9 and FIG. 1 indicate like elements. FIG. 8 andFIG. 9 illustrate the electronic assembly 10 after it is assembled. Inone configuration, the electronic assembly 10 may be assembled asfollows.

First, a semiconductor devices 48 is directly bonded to one or more coldplates or heat exchangers, such as first component 32 or the first heatsink 30 to form a chip assembly.

Second, the second sink 12 (or its first member 44 or 144), or boththrough one or more thermal pathways of the electronic assembly. In afirst example, a first thermal pathway represents a thermally conductivepath from the die (50, 150) via a metallic region 266 that is directlybonded to the first heat sink 30 or that is bonded with a thermallyconductive adhesive.

Third, the chip assembly can be placed through an appropriately sizedopening 20 in the circuit board 60. A circuit board 60 has an opening 20for receiving the semiconductor device 48. The lead frame 16 extends ator outward toward a board first side 76 of the circuit board 60. A boardsecond side 78 of the circuit board 60 is opposite the first side 76.Board conductive pads (18, 19) are on the board first side 76 of thecircuit board 60 to align with the corresponding terminals (52, 54, 56,58) of the lead frame 16 for electrical connection and mechanicalconnection with the corresponding terminals. In certain fabricationtechniques, the opening 20 in the circuit board 60 allowsafter-treatment of power circuit to meet creepage, clearance and highvoltage insulation requirements between semiconductor devices 48 andcold-plate. Exposure of chip assembly via the opening 20 in the circuitboard 60 can lower manufacturing cost or simplify manufacturingprocesses because the washing and cleaning processes, which are neededto eliminate residue left-over from lead-frame application, are easier,simpler; in some circumstances can be eliminated.

Fourth, the second component 35 is joined or secured to the firstcomponent 37 to form the first heat sink 30 with an interior volume 80for pumped fluid to circulate.

Fifth, the second member 42 is joined or secured to the first member (44or 144) to form the second heat sink 12 with an interior chamber 33 forpumped fluid to circulate.

FIG. 10 provides an example of how the electronic assembly 10 isincorporated into a hybrid vehicle with an internal combination engineand one or more drive motors 248. In FIG. 10, the electronics assembly10 uses active cooling. The electronic assembly 10 has an electricaltransmission line 251 connected to the input of an motor 248, such aselectric drive motor 248 to propel a vehicle. In one example, theelectronic assembly 10 receives direct current supply from a generator249 or energy storage device (e.g., battery) via one or more electricaltransmission lines 251. The generator 249 may be mechanically driven orrotated by a shaft (e.g., directly or indirectly the crankshaft) of theinternal combustion engine 241.

The internal combustion engine 241 may also provide mechanical,rotational energy or electrical energy to a pump 243 that circulatescoolant to one or more inlet ports 36 of the electronic assembly 10 andfrom one or more outlet ports 36 of the electronic assembly 10. Thecoolant is also circulated between the inlet 275 and outlet 276 of theengine water jacket (e.g., block or head) of the internal combustionengine 241. In one illustrative configuration, the output port 36 of theelectronic assembly 10 and the outlet 276 of the engine water jacket arecoupled via conduit 253 to a thermostatic valve 244 and cold temperaturebypass line 245. The thermostatic valve 244 opens at preset temperatureor preset temperature range to bring the radiator 246 into the coolingcircuit. Prior to opening of the thermostatic valve 244, the coolant isrouted through the cold temperature bypass line 245 back to the input277 of the pump 243 to bypass the radiator 246. After the thermostaticvalue opens at a preset temperature, one or more outlet ports 36 of theelectronic assembly 10 are coupled (directly or indirectly) to aradiator inlet 278 of a radiator 246 via conduit 253; similarly, theoutlet 276 of the engine water jacket is coupled via conduit 253 to theradiator 246. The radiator 246 has an outlet 279 that is coupled to thepump input 277 of the pump 243. The radiator 246 may be cooled by fan247 (e.g., electric fan 247), where the fan 247 is powered by a directcurrent bus via one or more transmission lines 251.

The electronic assembly supports either a separate coolant system froman internal combustion engine coolant loop or using the same coolantsystem of the internal combustion engine. For a separate coolant system,the maximum inlet temperature can be set to lesser maximum temperature(e.g., 70 degrees Celsius), whereas for the shared coolant system withthe internal combustion engine the coolant temperature can be set to agreater maximum temperature (e.g., 105 degrees Celsius). The maximumtemperature can be controlled via a thermostatic valve that opens toradiator and an associated fan, for example.

The electronic assembly of this disclosure does not require: (1) adirect bond copper (DBC) connection of a semiconductor device to aseparate intervening copper base plate with an adjacent, distinct heatsink mounted to contact the separate base plate with thermallyconductive grease, or (2) a direct bond copper connection of terminalsof the semiconductor devices 48 to the conductive traces or pads of thecircuit board. Here in one embodiment of this disclosure, thesemiconductor devices 48 (e.g., semiconductor chipsets) are directlybonded on one or more cold-plates (heat-exchangers), including the firstheat sink 30, or its first component 37, without any of use andinefficiency of thermally conductive grease; the terminals of thesemiconductor device 48 can be connected to corresponding conductivepads or traces on the circuit board via direct bonding or via aconductive adhesive, soldering, brazing, or welding. Directly bonding ofsemiconductor devices 48 with one or more cold-plates without any needof DBC, base plate, and thermal grease can significantly reduce thermalresistance between silicon junctions within the semiconductor device 48and coolant channels, interior, or chambers of the first heat sink 30,for instance.

The electronic assembly of this disclosure is well-suited fordouble-sided thermal management of the electronic assembly, such as aninverter. Double-sided thermal management has the potential tosignificantly reduce the thermal resistance for semiconductor devices,capacitors, power devices and components. Further, the electronicassembly facilitates active, thermal management, such as active,single-sided thermal management or double-sided thermal management ofthe electronic assembly.

The electronic assembly of this disclosure supports a reduced size,weight and cost of inverter because it supports surface-mountmanufacturing processes and a generally planar packaging configurationthat make the circuit boards amenable to mass, cost effectiveproduction.

Having described the preferred embodiment, it will become apparent thatvarious modifications can be made without departing from the scope ofthe invention as defined in the accompanying claims.

The following is claimed:
 1. An electronic assembly comprising: asemiconductor device having conductive pads on a device first side and ametallic region on a device second side opposite the first side; a leadframe for providing separate terminals that are electrically andmechanically connected to the conductive pads; a first heat sinkcomprising a first component having a mating side, a portion of themating side directly bonded with the metallic region of thesemiconductor device and having an opposite side opposite the matingside; and a circuit board having an opening, the semiconductor deviceand the lead frame extending at or outward toward a board first side ofthe circuit board, a board second side of the circuit board opposite thefirst side, a plurality of board conductive pads being on the boardfirst side of the circuit board to align with the correspondingterminals of the lead frame for electrical connection therewith.
 2. Theelectronic assembly according to claim 1 wherein an auxiliary metallicregion comprises a central metallic region on the device first side. 3.The electronic assembly according to claim 2 wherein the conductive padsare arranged at or near a perimeter of the semiconductor device outwardfrom the auxiliary metallic region.
 4. The electronic assembly accordingto claim 1 wherein the opposite side of the first heat sink comprisesfirst protrusions for heat dissipation.
 5. The electronic assemblyaccording to claim 1 wherein the board conductive pads comprise metalliclayers of greater thickness than other conductive traces on the circuitboard.
 6. The electronic assembly according to claim 1 wherein the boardconductive pads comprise copper or copper alloy pours.
 7. The electronicassembly according to claim 1 wherein directly bonded means that themetallic region and the first component of the heat sink are fused,brazed or welded to form an electrical and mechanical connection.
 8. Theelectronic assembly according to claim 1 wherein the heat sink islocated at or below the board second side of the circuit board.
 9. Theelectronic assembly according to claim 1 further comprising: a secondheat sink comprising a first member overlying a device first side of thesemiconductor device, such that the semiconductor device has thermalpathways for heat transfer or dissipation on both the device first sideand the device second side.
 10. The electronic assembly according toclaim 9 wherein a thermal interface material comprises a dielectricmaterial between the first member of the first heat sink and a terminalof the semiconductor device, wherein the terminal is electrically andmechanically connected to one or more conductive pads on the devicefirst side.
 11. The electronic assembly according to claim 9 wherein thesecond heat sink further comprises: a second member that mates with thefirst member to form an interior chamber; a plurality of secondprotrusions populating the interior chamber and generally spaced apartfrom each other; an inlet and an outlet for communication with theinterior chamber to circulate a liquid coolant within the interiorchamber.
 12. The electronic assembly according to claim 1 wherein thefirst heat sink comprises: a second component with a recess, the secondcomponent mating with the first component to form an interior volume; aplurality of first protrusions of the first member populating theinterior volume and generally spaced apart from each other; and an inletand an outlet for communication with the interior volume to circulate aliquid coolant within the interior volume.
 13. The electronic assemblyaccording to claim 12 wherein the first component comprises a lid withthe thermal dissipation members extending from one end, where eachprotrusion comprises a ridge or elevated region that extends outwardfrom a base surface of the lid.
 14. The electronic assembly according toclaim 1 further comprising a current sensor above a conductive strip onthe circuit board.
 15. The electronic assembly according to claim 1wherein the current sensor is surrounded by a metallic shield associatedwith the circuit board.
 16. The electronic assembly according claim 1wherein the lead frame comprises an output terminal that has aninterfacing surface that is bonded to the conductive pads of the deviceand an auxiliary metallic region on the device first side.
 17. Theelectronic assembly according to claim 16 wherein the output terminal isconnected to a corresponding conductive strip on the circuit board,where the conductive strip has sufficient size to promote secondary heatdissipation from the output terminal.
 18. The electronic assemblyaccording to claim 16 wherein the output terminal has a notch in aninterfacing surface of the output terminal.